Loop debugging activity

The following program should allow the user to input as many things as they want until they stop. Each time it is supposed to repeat what the user said, can you fix it?

import java.util.Scanner;

public class EndlessStrings {
    public void main (String[] args)
    {
        Scanner keyboard = new Scanner(System.in);

        String userInput = "";

        userInput = keyboard.next();

        while ( userInput != "" )
        {
            System.out.println(userInput);

        }
    }
}